Stabilization of lube oil

ABSTRACT

This invention relates to a method for improving the oxidative stability of hydrocarbon lubricating oils by contact with a gas containing free oxygen in the presence of a solid basic refractory oxide catalyst, characterized by the presence therein of a minor proportion of alkali metal, under specified conditions of temperature and pressure.

United States Patent 1 Yan [111 3,883,416 51 May 13, 1975 STABILIZATION 0F LUBE OIL [75] Inventor:

[73] Assignee: Mobil Oil Corporation, New York,

[22] Filed: Oct. 9, 1973 [21] Appl. No.: 404,466

Tsoung Y. Yan, Trenton, NJ.

[52] US. Cl. 208/3; 208/255; 208/DlG. 002 [51] Int. Cl. C07c 27/10 [58] Field of Search 208/3, DIG. 002, 255

[56] References Cited UNITED STATES PATENTS 2,786,803 3/1957 Whitney 208/3 2,882,243 4/1959 Milton 208/DlG. 002

Primary Examiner-Veronica OKeefe Attorney, Agent, or Firm-Charles A. Huggett;

Raymond W. Barclay [57] ABSTRACT 10 Claims, No Drawings STABILIZATION OF LUBE OIL BACKGROUND OF THE INVENTION ble to oxidative instability. Typical of the stocks which may be treated in accordance with the method described herein are shown below:

1. Field of the Invention This invention pertains to production of lubricating oils, of petroleum origin, characterized by improved oxidative stability.

2. Description of the Prior Art Petroleum lubricating fractions produced by conventional refining techniques including distillation, acid treatment, clay treatment, solvent refining, etc. often possess unsatisfactory oxidation stability in spite of the refining procedures which have been employed. Such unsatisfactory oxidation stability encountered in lube oil fractions frequently gives rise, upon subjection to oxidation, to excessive discoloration, formation of acidic materials and production of heavy viscous sludges and resins which deposit on the surface which it is desired to lubricate.

Due to the lubricant oxidative stability requirements of new larger machinery, engines and the like, feedstocks which were formerly satisfactory for lubricant production are presently unsuitable or at best marginal for such uses. Thus, at a time when overall lubricant demands are increasing and becoming more stringent, the amount of suitable lubricant petroleum feedstock is being diminished due to the oxidative lubricant stability requirements of modern usage.

While some antioxidant additives have been developed as an aid in improving lubricant oxidative stability, such additives have been expensive to' employ, particularly in large scale operations.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a method for improving the oxidative stability of a hydrocarbon lubricating oil which comprises contacting said oil with a gas containing free oxygen, such as air, in the presence of a solid basic refractory oxide catalyst characterized by an alkali metal content of at least about 2 percent by weight. Contact is accomplished at a temperature generally in the range of 150 to 550F., preferably between about 200 and 350F., at a pressure between atmospheric and 500 psig and at a liquid hourly space velocity of between about 0.1 and about volumes/volume of catalyst/hour.

The feedstocks undergoing treatment in accordance with the method of the invention are those petroleum lubricant stocks resulting from conventional refining such as distillation, followed by solvent extraction, e.g., with furfural, and dewaxing, e.g., with methyl ethyl ketone. The oils are identified according to the source of their crude oil and physical properties. Mid- Continental stocks appear to be particularly suscepti- The feed stock of the type above described is, in accordance with the method of the invention, contacted with a gas containing free oxygen. Such gas is suitably air, but may be oxygen alone or oxygen mixed with dil' uent gases such as nitrogen, helium, argon or other inert gases. Generally when utilizing air, such gas is cofed with the oil feed stock at a rate of at least 2 volumes of air per volume of oil. When utilizing a gas containing free oxygen, other than air, corresponding suitable adjustment in the volume of such gas is contemplated such that the amount of oxygen present is at least about 0.4 volume of oxygen per volume of oil. Contact between the feed stock and the gas containing free oxygen may be effected in any suitable manner including concurrent or counterconcurrent contact in the catalyst bed.

The catalyst employed herein is a refractory basic solid having a minimum alkali metal content of approximately 2 weight percent. A wide variety of catalytic materials may be used including alkali metalcontaining alumina, silica, crystalline aluminosilicates, both synthetic and natural, ores, clays, such as montmorillonite, and metal ferrites, such as zinc ferrite. Representative of suitable catalysts are the alkali metal crystalline aluminosilicates of the X and Y type. Such materials may include the sodium forms of these synthetic crystalline aluminosilicates in the as synthesized condition or compositions resulting from ion exchange or impregnation with other alkali metals such as potassium, rubidium or cesium. Other feasible catalysts include suitable supports such as alumina or silica having impregnated thereon an alkali metal in the amount of at least 2 weight percent and preferably between about 4 and about 30 weight percent. Representative of such compositions are theta alumina containing about 5 weight percent sodium and silica gel impregnated with sodium and/or rubidium. Other suitable catalysts are clays of the montmorillonite type which are particularly applicable and attractive for use in the present process due to their inexpensive origin. Another catalyst which has been found=to be effective is zinc ferrite containing about 5 weight percent of potassium. These catalysts are calcined, generally by heating at a temperature of between about 500 and about l,000F. for a period of approximately 3 hours or longer and may thereafter be sulfided by contacting with hydrogen sulfide at a temperature of between about 300 and about 700F. for a period of time generally in the range of about 2 to about 10 hours. The catalyst is generally in particle form, preferably having a particle size of between about 4 and about 30 mesh. The amount of catalyst employed will generally be in the range of from about 0.01 to about 10 weight percent of the feed stock undergoing treatment. In a fixed bed operation, the oil/catalyst volume ratio will be in the approximate range of 10 to 10,000.

Contact between the feedstock, the oxygen free gas and the catalyst is generally accomplished by continuously passing the feedstock and the oxygen free gas through a bed of the catalyst. Alternatively, the operation may be carried out as a batch process wherein the feedstock is contacted with the catalyst and air or other oxygen containing gas is bubbled into such mixture, after which the treated oil product is removed from the catalyst by any suitable means such as by filtration or distillation to obtain the treated oil product or desired fractions thereof as distillates while leaving undesired reaction products in the residue.

The temperature of treatment is generally between about 150 and about 550F. Particular preference is accorded a temperature in the approximate range of 200 to 350F. since it has been established that treatment under the latter temperature conditions produces a product characterized by oxidative stability without detrimentally affecting the color of the resulting product. Operation at a temperature above 350 and up to 550F. affords a resultant product characterized by improved oxidative stability but it has been observed in some instances that the resulting product has a generally undesired dark color. The pressure at which the described process is carried out is generally atmospheric but may be within the range of from atmospheric up to about 500 psig. Contact between the feed stock and the catalyst generally takes place at a liquid hourly space velocity of between about 0.1 and about 10 volumes of feed stock per volume of catalyst per hour.

DESCRIPTION OF SPECIFIC EMBODIMENTS The following examples will serve to illustrate the invention without limiting the same:

EXAMPLE 1 A catalyst was prepared by impregnating 10 grams of sodium zeolite X with 20 cc of rubidium acetate solution (containing 0.87 gram of RbC l-I O to a rubidium level of 5 weight percent. The impregnated material was then calcined to 1,000F. at a rate of lC./minute.

A lube oil stock having the following properties:

Gravity, API 30.0 Pour Pt., F. 5 Flash Pt., F. 425 Sulfur, wt. 0.27 Nitrogen, wt. 0.007 Aniline Point, F. 219.1 Viscosity, S.U.S. at 100F. 232 Viscosity Index 97 ASTM Color W:

was passed over the above-described catalyst in an upflow reactor at 1 Ll-ISV at atmospheric pressure and at a temperature of 400-550F. Air was co-fed with the oil at rates of and Sec of air/cc of oil. The oil products were stripped of any light products and water to an equivalent temperature of 650F. and tested for oxidative stability.

The test to which the oil product was subjected involves placing a 25 gram sample of the test oil in a 200 mm. X 25 mm. test tube. The test oil has immersed therein (a) 15.6 sq. in. of sand-blasted iron wire, (b) 0.78 sq. in. of polished copper wire, (c) 0.87 sq. in. of polished aluminum wire and (d) 0.167 sq. in. of a polished lead specimen. The oil sample was heated to a temperature of 325F. and maintained at such temperature for a period of 40 hours while dry air was passed therethr'ough at a rate of 5 liters per hour. The change in neutralization number and kinematic viscosity before and after the oxidation are recorded and the weight loss of the leaded speciment is obtained. The improved oxidative stability of the treated oil is shown by the low increase in kinematic viscosity and low increase in neutralization number. The change in kinematic viscosity reflects the rate of production of heavy polymerized hydrocarbon materials due to oxidation, such as sludges, which increase the viscosity. The increase in neutralization number reflects an increase in content of acidic materials in the treated oil.

The results of treating the above oil and testing are shown in the following table:

A catalyst of sodium X was employed in treatment of the oil feed described in Example 1 at a temperature of 300 to 400F., atmospheric pressure and a liquid hourly space velocity of 1.

The resulting oil product was tested as described in the above test with the results shown hereinafter in Table II.

EXAMPLE 3 A catalyst of theta alumina containing 5 weight percent of sodium was used in treatment of the oil of Example l at a temperature of 200 and 250F., at atmospheric pressure and a liquid hourly space velocity of l.

The resulting oil product was tested as described in the above test with the results shown hereinafter in Table II.

EXAMPLE 4 A catalyst of cesium zeolite Y was obtained by ion exchange of sodium Y with cesium acetate to a cesium level of 5 percent by weight. This catalyst was used in treating the oil of Example 1 at a temperature of 200F., atmospheric and liquid hourly space velocity of l. The resulting oil product was tested as described in the above test with the results shown hereinafter in Table II.

EXAMPLE 5 Acatalyst of silica gel impregnated with 5 weight percent of rubidium and 5 weight percent of sodium was employed in treating the oil feed described in Example 1 at a temperature of 300 and 200F. at atmospheric pressure and liquid hourly space velocity of 1.

The resulting oil product was tested as described in the above test with the results shown hereinafter in Table 11.

EXAMPLE 6 EXAMPLE 7 A catalyst of zinc ferrite containing 5 weight percent of potassium was employed in treating the oil feed described in Example 1 at a temperature of 200F., atmospheric pressure and liquid hourly space velocity of l.

The resulting oil product was tested as described in the above test with the results shown hereinafter in Table 11.

EXAMPLE 8 A sample of sodium Y zeolite was exchanged with rare earth chlorides repeatedly to a sodium level of about 0.5 weight percent. This catalyst was employed in treating the oil feed described in Example 1 at a temperature of 200F., atmospheric pressure and liquid hourly space velocity of 1.

The resulting oil product was tested as described in the above test with the results shown hereinafter in Table II. The high figures observed for change in kinematic viscosity and neutralization number indicate that the acidic REY product is not an effective catalyst for this application.

Treatment was carried out at atmospheric pressure,

a liquid hourly space velocity .of 1 and temperatures ranging from 150F. to 350F. The feed and the results are shown in Table 111 below:

TABLE 111 Run Number Feed l3 l4 l5 l6 Treating Condition Temperature. F. 200 300 250 150 Product Inspection Color 1% 1% 2 1% 1% Oxidation Test (325F., Hrs) AKV% 17 1O 8 9 10 ANN 3.3 1.8 1.9 2.1 2.2 Lead Loss 3.4 1.2 1.8 0.8 Bromine No. 0.9 1.0 1.0 1.0

It will be seen from the above data that the oxidative stability of the lube oil feed was considerably improved by reacting it with air over the specified refractory basic solids. The mild treating conditions coupled with the relatively simple procedure of the described treating technique is particularly applicable in upgrading marginal stocks with respect to improvement in oxidative stability.

1 claim:

1. A method for improving the oxidative stability of a hydrocarbon lubricating oil which comprises contacting said oil with a gas containing free oxygen and a solid basic refractory oxide catalyst characterized by an alkali metal content of between about 2 and about 30 percent by weight at a temperature in the range of about 150 to about 550F., at a pressure between at- TABLE 11 Example 2 3 4 5 6 7 8 Run Number Feed 3 4 5 6 7 8 9 10 ll 12 Catalyst CsY Description NaX Theta Alumina CsY Silica Gel NaX Zinc REY (Na 5%) (Via Ex) Rb (5%) Ferrite Na (5%) K (5%) Treatment Calcined Calcined Calcined Calcined Sulfided Calcined Calcined Treating Condition Temperature. F. 300 400 200 250 200 300 200 200 200 200 Product'lnspection Color 1 /2 2 7 /2 2 2% 2% 3% 2 2 2% 2% Oxidation Test (325F, 40Hr.)

AKV, 269 57 64 49 47 52 64 63 38 44 147 ANN 21 5.4 5.4 8.2 8.2 8.2 10.1 8.5 7.1 7.6 14.2 Lead Loss 320 9.2 7.5 1.6 0.6 19.9 12.4 1.8 2.7 70.2 Bromine Number 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.5 0.6 0.6 0.8

EXAMPLE 9 mospheric and 500 psig and at a liquid hourly space ve- A sample of montmorillonite clay was impregnated with K CO to a potassium level of 5 percent. The resulting catalyst was employed in testing an Arabian light stock having the following properties:

locity of between about 0.1 and about 10 volumes/- volume of catalyst/hour.

2. The method of claim 1 wherein the temperature is between about 200 and 350F.

3. The method of claim 1 wherein the gas containing free oxygen is air.

4. The method of claim 3 wherein air is contacted with said oil at a rate of at least 2 volumes of air per volume of oil.

5. The method of claim 1 wherein said catalyst is an alkali metal crystalline aluminosilicate.

6. The method of claim 1 wherein said catalyst is montmorillonite clay.

7 8 7. The method of claim 1 wherein said catalyst is silferrite containing alkali metal. lea gel mpregnated alkah metal 10. The method of claim 1 wherein said catalyst is so- 8. The method of claim 1 wherein said catalyst is alumina impregnated with alkali metal.

9. The method of claim 1 wherein said catalyst is zinc dium zeolite X. 

1. A METHOD FOR IMPROVING THE OXIDATIVE STABILITY OF A HYDROCARBON LUBRICATING OIL WHICH COMPRISES CONTACTING SAID OIL WITH A GAS CONTAINING FREE OXYGEN AND A SOLID BASIC REFRACTORY OXIDE CATALYST CHARACTERIZED BY AN ALKALI METAL CONTENT OF BETWEEN ABOUT 2 AND ABOUT 30 PERCENT BY WEIGHT AT A TEMPERATURE IN THE RANGE OF ABOUT 150* TO ABOUT 550*F., AT A PRESSURE BETWEEN ATMOSPHERIC AND 500 PSIG AND AT A LIQUID HOURLY SPACE VELOCITY OF BETWEEN ABOUT 0.1 AND ABUT 10 VOLUMES/VOLUME OF CATALYST/HOUR.
 2. The method of claim 1 wherein the temperature is between about 200* and 350*F.
 3. The method of claim 1 wherein the gas containing free oxygen is air.
 4. The method of claim 3 wherein air is contacted with said oil at a rate of at least 2 volumes of air per volume of oil.
 5. The method of claim 1 wherein said catalyst is an alkali metal crystalline aluminosilicate.
 6. The method of claim 1 wherein said catalyst is montmorillonite clay.
 7. The method of claim 1 wherein said catalyst is silica gel impregnated with alkali metal.
 8. The method of claim 1 wherein said catalyst is alumina impregnated with alkali metal.
 9. The method of claim 1 wherein said catalyst is zinc ferrite containing alkali metal.
 10. The method of claim 1 wherein said catalyst is sodium zeolite X. 